ON-SKY CHARACTERIZATION ITEMS
Note: in case of measurement of sky properties, the measurement listed is
to be carried out in every appropriate filter. Repeatability of filter
placement is probably a good thing to test also - this can be done in a
number of the tests below I guess **** yes definitely ****
DETECTOR NOISE PROPERTIES
The detectors will be being used in a new mains power environment,
attached to a telescope, and may have noise properties different to those
measured in the lab. The difference needs to be characterized so that its
impact on data reduction can be assessed. Also remeasure crosstalk matrix
in the on-telescope state. Bad pixel stability should be assessed as soon
as possible so we should be taking bias and dark frames from the very
start.
**** include re-assessing the repeatability and level of the reset anomaly/
dark stability ****
SKY EMISSION
Brightness, time variation, spatial scales of the emission. Effect of
large spatial offset to a "sky" position. Sky brightness vs. distance from
Moon (check for additional contribution from scattered light). Sky
brightness as function of zenith distance.
FRINGING
Fringe amplitude and stability during change of sky brightness. Variation
time and spatial scales, speeds of motion.
SENSITIVITY
Need an early measurement of the sensitivity limit in the standard
observing modes. Also should compare coadded images of the same field
taken on widely-separated nights. Quantify overheads in standard observing
modes.
BACKGROUND LIMIT
Check early what exposure time is needed to reach background limit.
COSMIC RAYS
Long exposure to pick up a lot of CRs - test whether DR rejects them.
PERSISTENCE
Check in a field with a range of point-source brightnesses
**** possibly repeat at further intervals to check on temporal stability
of effect ****
FLAT FIELD
Dome flats, frames taken close to twilight - usable ? Nonlinearity
measurements in here too (might be difficult to always do at the same time
since STARE mode needed for nonlinearity measurements). Vignetting
function and its motion if any. Tests of different flat fielding
algorithms.
**** need to assess stability of flats since impacts on data taking and
reduction strategy ****
**** nonlinearity measurements are done using dome flats so not quite sure
what the above comments is referring to ****
**** will we have a means taking of dome flats/linearity checks with stable
illumination source and screen ? ****
SCATTERED LIGHT
Observe a field with large numbers of stars. See if we can measure the
scattered light.
**** may be easier to interpret with a few bright stars ****
CALIBRATION DETAILS
Place a UKIRT faint standard on each chip independently (possibly even in
each of the different channels on each chip?). Visit a number of standard
fields.
ASTROMETRY
Dead-reckoning coordinate system - first go.
**** should be easy enough once we figure out which way up the detectors
have been read out, also add refining the WCS constants and in
particular the radial distortion model since needed later for more accurate
astrometry ****
**** could use this to check microstepping accuracy - is it n+1/2 pixel ? ****
GUIDING
Guiding in crowded fields needs to be tested. **** and in the middle of
large extended objects ****
STANDARDS
**** we would like to include first epoch measurements of secondary standard
fields as early as possible - not technically on-sky characterisation, but
we would like to see a commitment to devote significant time to standards in
these early WFCAM phases ****
**** do we want to include a mesostep sequence early on ? ****